In general, the present disclosure relates to an imaging device, a driving method and an electronic apparatus. More particularly, the present disclosure relates to an imaging device capable of repressing deteriorations of a photoelectric conversion film employed in the device, a driving method for driving the device and an electronic apparatus employing the device.
In a solid-state imaging device such as typically a CCD (Charge Coupled Device) or a CIS (CMOS Image Sensor), the quantity of light incident to a photodiode included in a pixel employed in the device decreases due to miniaturization of the pixel. It is thus difficult to obtain a sufficient sensitivity.
In addition, in the solid-state imaging device, elementary-color filters for the three elementary colors, that is the red, blue and green colors, are widely used. The elementary-color filters are laid out to form the so-called Bayer array which is a checker board design. In the solid-state imaging device employing such color filters, light is inevitably absorbed by the filters. Thus, the efficiency of the utilization of the light decreases and, in addition, a false color may be generated during demosaic processing in some cases.
As is disclosed in documents such as Japanese Patent Laid-open No. 2006-278446, on the other hand, there has been proposed a solid-state imaging device which is configured to employ, for every pixel of the device, a first layer formed on the upper surface of a silicon substrate to serve as a photoelectric conversion section and a second layer formed at a different depth inside the silicon substrate to serve as a photodiode. Inside the silicon substrate, the solid-state imaging device utilizes the fact that the wavelength of absorbed light varies along the depth direction. That is to say, the solid-state imaging device is configured to employ the first layer serving as a photoelectric conversion section configured to carry out a photoelectric conversion process on light having a specific wavelength and the second layer serving as a photodiode for carrying out a photoelectric conversion process on other light having a wavelength different from the specific wavelength.
Thus, the solid-state imaging device disclosed in Japanese Patent Laid-open No. 2006-278446 does not require a color filter so that the solid-state imaging device is capable of avoiding decreases caused by the color filter as decreases of the efficiency of the utilization of light. In addition, since the existing demosaic processing is also no longer necessary, generation of a false color can also be avoided as well.
By the way, the photoelectric conversion section formed on the upper surface of the silicon substrate is configured to include a photoelectric conversion film whose lower and upper surfaces are transparent electrodes sandwiching the film. For example, on the lower surface of the photoelectric conversion film employed in the photoelectric conversion section, pixel electrodes are laid out for their respective pixels, being separated away from each other. On the upper surface of the photoelectric conversion film employed in the photoelectric conversion section, on the other hand, an opposite electrode common to all the pixels is provided, being shared by the pixels. In addition, in the existing solid-state imaging device, the electric potential appearing at the common opposite electrode shared by all the pixels is sustained at a constant level in the course of an operation to drive the pixels. In this state, an electric field having a fixed direction is applied to the photoelectric conversion film sandwiched by the pixel electrodes laid out on the lower surface of the film and the common opposite electrode provided on the upper surface of the film.